The purpose of this proposed research is to physically characterize rat liver ribosomes and ribosomal RNA. Using suitable physical techniques, the diffusion coefficient, sedimentation coefficient, intrinsic viscosity, density increment, extinction coefficient and molecular weight are to be determined for the 60S and 40S ribosomal subunits and the 28S and 16S rRNA derived therefrom. Molecular weights will be determined using both sedimentation equilibrium and sedimentation-diffusion methods. The approximate size, shape and hydration will be determined by coupling sedimentation, diffusion and viscosity results.